1. Field of the Invention
The present invention relates to a power supply device that supplies electric power to a processing device, and a communication apparatus that performs a communication processing.
2. Description of the Related Art
In conventional art, electric apparatuses such as a communication apparatus or server apparatus are each provided with a power supply device that supplies electric power to ICs and the like that execute various types of processings; and electric power must be stably supplied to this power supply device at all times. Particularly, voltages outputted to the ICs and the like need to be regulated at a constant level.
FIG. 1 is a schematic configuration diagram of a power supply device that supplies electric power to an electric apparatus.
The power supply device 10 illustrated in FIG. 1 is an analog control type power supply device using analog elements such as an amplifier and a comparator, which regulates the voltage outputted to ICs and the like.
The power supply device 10 includes a voltage detection circuit 11, error amplifier 12, compensation circuit 13, reference oscillator 14, comparator 15, switching element 16 and smoothing filter 17.
First, the voltage detection circuit 11 detects power source output voltage Vout currently outputted from the power supply device 10 to ICs and the like. The detected output voltage Vout is sent to the error amplifier 12. The error amplifier 12 amplifies and outputs a difference between output voltage Vout and reference voltage V0. The compensation circuit 13 regulates amplification voltage Vg outputted from the error amplifier 12 at a value suitable for the sensitivity of the comparator 15.
The reference oscillator 14 outputs voltage signal Vp of a sawtooth waveform at a given frequency. The comparator 15 compares voltage signal Vp of a sawtooth waveform outputted from the reference oscillator 14 with amplification voltage Vg regulated by the compensation circuit 13, and sends a control signal to the switching element 16, wherein the control signal turns on when voltage signal Vp of a sawtooth waveform is smaller than amplification voltage Vg, and turns off otherwise.
ON/OFF control of the switching element 16 is performed by use of the control signal sent from the comparator 15, so that the pulse width of input voltage Vin inputted to the power supply device 10 is regulated; and the smoothing filter 17 executes a smoothing processing. Consequently, output voltage Vout having a regulated voltage value is outputted from the power supply device 10 to the electric apparatus. For example, when output voltage Vout detected by the voltage detection circuit 11 lowers, the difference calculated by the error amplifier 12 between output voltage Vout and reference voltage V0 increases. As a result, voltage signal Vp of a sawtooth waveform becomes smaller than amplification voltage Vg and thus “ON” time of the control signal outputted from the comparator 15 lengthens to increase the pulse width of input voltage Vin. Thus, output voltage Vout rises.
As described above, control is performed in the power supply device 10 so that the output voltage outputted to the processing section is kept constant.
In recent years, as power saving of electric apparatuses and miniaturization of batteries progress, there is increasing demand for lower-voltage application of various components and ICs etc. constituting an electric apparatus. Thus, the current flowing into these components and ICs tends to increase. Further, in the communication apparatuses, server apparatuses and the like, the current flowing into an IC which executes a communication processing can sharply increase in such a manner that interlocks with the traffic state of communication; in this case, the originally low voltage applied to the IC may further lower and fall below a minimum voltage allowing execution of the communication processing, thus causing a trouble such as signal interruption.
In this regard, Japanese Patent Laid-Open No. 9-154275 has disclosed a technique of providing a power supply device with a capacitor for soft start and thereby reducing a sharp change in current at the time of turning on or turning off the power supply. When current is varied smoothly at the time of turning on or turning off the power supply, the internal circuit can be prevented from being overloaded by a peak current during start-up of the power supply, or from malfunctioning due to voltage reduction; these are now posing a problem for electric apparatuses for which large-current application has progressed.
However, the technique described in Japanese Patent Laid-Open No. 9-154275 cannot cope with a sharp change in current caused by an increase in load in a processing intermittently performed, such as a communication processing.
In the conventional analog control type power supply devices, the switching frequency is raised to improve the response of power supply; power supply is regulated in a manner following a sharp change in processing load. However, with only this regulation of switching frequency, it is difficult to further improve the response of power supply.